The residential drinking water for forty-one million Americans in twenty-four major metropolitan areas contains pharmaceutical compounds. The human health effects of long-term, chronic exposure to trace levels of these hormones, endocrine-disrupting compounds, painkillers, and antibiotics are not yet fully understood, although the impact on aquatic life has been observed as changes in reproductive health and function. The importance of this potential threat to human health is the subject of much recent research and investigation highlighted by two late-2008 conferences sponsored by the National Institute of Environmental Health Sciences regarding pharmaceuticals and personal care products in the environment.
These compounds are present at minute, yet potentially significant, concentrations. Existing tools that can measure these very low concentrations—e.g., liquid chromatography with mass spectroscopy (LC-MS)—are expensive, complex, laboratory-based instruments. Current portable monitoring tools cannot even approach measuring parts per billion, let alone the parts-per-trillion levels of pharmaceuticals found in drinking water. At the same time, our water sources are threatened by numerous other pollutants with regulatory limits at the parts-per-billion level: agricultural run-off, heavy metals, military remnants, and industrial waste. The ability to monitor our water supply at the parts-per-billion level at the source or in the field would vastly improve the capabilities of water suppliers. This ability will in turn allow water suppliers to increase monitoring frequency, to implement remediation steps, and to focus research efforts on understanding of the health effects of chronic exposure.
Laboratory detection equipment such as embedded surface-enhanced Raman spectroscopy (eSERS) can address this deficiency by measuring compounds in aqueous solution at better than one part per billion. This embedded detection approach relies upon geometric constraints within a microfluidic channel to trap gold nanoparticles, creating a region of extreme nanoparticle density—i.e., maximum surface area in a minimum volume—required for the eleven to fifteen order-of-magnitude enhancement of Raman signal.
The presence of pharmaceuticals in the environment has been documented since the 1980s. Recent surveillance studies have brought this concern to the forefront, highlighting the widespread impact upon the US population. It has been reported that at least 41 million Americans across 24 major metropolitan areas have detectable levels of pharmaceuticals in their drinking water. Multiple US Geological Survey studies and reports since the late 90's have demonstrated the presence of contaminants in ground and surface water. Moreover, the NIEHS sponsored two late-2008 conferences regarding pharmaceuticals and personal care products in the environment, the US EPA launched Information Collection Request for health care facilities regarding unused pharmaceuticals, and the National Academy of Sciences had a December 2008 workshop on screening risk from pharmaceuticals in drinking water.
The health effects of these trace compounds on humans are not well understood, although reports regarding the impact on non-target species are widely known. Many fish experience reproductive problems, with male fish producing female proteins and female fish growing male reproductive organs. In some locations downstream from wastewater treatment facilities, the ratio of males to females is wildly skewed, even though the populations are normal upstream.
The challenge with understanding the health effect on humans is the time-scale at which an effect might occur and the wide range of potential contaminants at minute concentrations over a large area. A recent study found 34 pharmaceuticals and other organic wastewater contaminants in a New Jersey stream downstream from a wastewater-treatment facility. These chemicals included antibiotics (triclosan and sulfamethoxazole), nicotine metabolites (cotinine), decongestants (diphenhydramine), and analgesics (acetaminophen). Philadelphia discovered 56 pharmaceuticals and by-products in treated drinking water, including epilepsy and mental illness medications in the tens of parts per trillion range.
Pharmaceuticals are not the only contaminant of concern in drinking water; the total number of potential contaminants is staggering. Industrial waste and agricultural run-off are both frequently detected in surface water, with levels regulated by the EPA. Some compounds are widely used in industrial or agricultural settings, such as atrazine to control broadleaf weeds—which has been reported to cause reproductive problems in non-target species (including humans). Some compounds may be intentionally added to food or water, such as the addition of melamine to infant formula—a chemical that has been added nefariously to Chinese products and inadvertently to American products. Other compounds leach from storage containers, such as bisphenol A (BPA) from plastic bottles. A portable instrument that could measure these compounds at the part-per-billion level would be valuable to water suppliers, regulators, and consumers world-wide to maintain safe supplies, increase monitoring frequency and accuracy, and provide comfort that our water is safe to drink.
The first line of defense for protecting the water supply—and ultimately, human health—from pharmaceuticals and other contaminants is tools to rapidly and accurately measure trace levels of compounds in the field or at the source. Unfortunately, water analysis at the required accuracy with a portable instrument is currently not possible. Current portable instruments either measure overall water quality or measure water constituents. Tools that measure water quality focus on pH, turbidity, and total dissolved solids to provide a generic measure of water cleanliness. These tools are valuable for the speed at which they provide confidence, but do not measure actual water contaminants. Tools that measure water constituents primarily focus on UV/vis spectrometry or colorimetry. Both analytical methods are limited to measuring parts per million, far from the regulatory limits of many compounds, and even farther from the concentration of pharmaceuticals in drinking water.
Not only are the total number of potential contaminants staggering, but so are also the number of required analytical techniques. Analysis of specific analytes at minute levels within a water sample requires complex, expensive laboratory equipment. A variety of laboratory techniques exist, with the EPA providing a list of available and approved techniques for compounds of concern. The American Public Health Association, American Water Works Association, and Water Environmental Federation publish “Standard Methods for the Examination of Water and Wastewater”, an extensive treatise on water analysis methodology. Most analytes require a two-step technique: chemical separation followed by analytical spectroscopy. This two-step approach is essential when a mixture is considered. The combination of signals from multiple analytes will wash out the signal from any individual compound. Consequently, field samples are frequently sent to a laboratory for chromatographic separation followed by some form of analytical detection.
Separation is critical for reliable, accurate detection. But, without adequate detection techniques, separations are of little value. A variety of methods are used in water analysis. Ultraviolet-visible (UV/vis) spectroscopy is popular, as the technique is simple and quantitative. However, UV/vis cannot detect material concentrations much better than one part per million, limiting its value to high-level screening of basic ions or gross contaminants. Other optical methods such as fluorescence, refractive index measurements, or colorimetry either require specialized chromaphores or similarly lack sensitivity.
Mass spectrometry (MS) is a widely used and popular approach with the ability to measure at the required sensitivities. MS is a standard add-on to liquid chromatography systems (LC-MS), although at a cost of tens of thousands of dollars. MS requires ionization of the analyte of interest, breaking the compound into various subcomponents. These charged components pass through a magnetic field and are differentially deflected onto a detector array. The distribution across the detector array is a function of the charge-to-mass ratio. Various derivatives that are more sensitive or more accurate have been developed, but it is possible to detect sub-ppb using MS. On the other hand, the disadvantages of MS are 1) high cost, and 2) the impracticality of developing a portable, handheld system. These limitations keep MS as a laboratory instrument for trained operators.
What is needed is a portable, rapid measurement analysis instrument to allow water suppliers to 1) determine more quickly which compounds are present, 2) choose remediation steps, 3) add specific monitoring of ground and surface water, 4) increase studies of the human health effects of specific pharmaceuticals, and 5) eliminate the source through targeted public educating on proper disposal of prescription and non-prescription drugs.